A Waveguide (1) for transmitting a radio frequency signal with a hollow waveguide body (2) extending along a central axis (3) between a first open end (4) and a second open end (5). A body wall (8) of the hollow waveguide body (2) is fabricated from an electrically conductive material and encloses a waveguide cavity of the waveguide body (2). At least in a first section (12) of the waveguide (1) adjacent to the first end (4) of the waveguide body (2) the waveguide (1) comprises a first pair (6) and a second pair (7) of opposing ridge elements of the electrically conductive material. Each of the respective ridge elements arranged at the body wall (8) of the waveguide body (2) is projecting inwardly from the body wall (8) and extending along the central axis (3). Each of the ridge elements comprises a ridge tail surface (9) that is closer to the central axis (3) than the adjacent parts of the body wall (8). At least in the first section (12) an adapting element (10) comprising a dielectric material (11) with a relative permittivity larger than air is arranged in between the opposing ridge tail surfaces (9) of the first pair (6) and the second pair (7) of ridge elements.